本文選題：膜污染 + CFD模擬��； 參考：《天津工業(yè)大學(xué)》2017年碩士論文

【摘要】：膜污染限制了中空纖維膜在水處理中的進(jìn)一步應(yīng)用,而水力反洗和氣體沖洗能夠有效地緩解外壓浸沒(méi)式中空纖維膜系統(tǒng)中的膜污染問(wèn)題。本文通過(guò)計(jì)算流體力學(xué)(CFD)模擬手段來(lái)研究反洗過(guò)程中膜面污染層的變化情況,以及氣體沖洗過(guò)程中剪切力對(duì)膜污染去除的影響。在模擬的過(guò)程中,放置在幾何體內(nèi)的膜組件反映了中空纖維膜的真實(shí)尺寸,并且在反應(yīng)器的底部有一個(gè)簡(jiǎn)化的曝氣裝置用來(lái)模擬氣體沖洗過(guò)程。此外,膜絲被設(shè)置成多孔介質(zhì)區(qū)域而非無(wú)滑移壁面。首先,利用CFD數(shù)值模擬,研究了水力反洗過(guò)程中膜面污染層的變化情況。假設(shè)過(guò)濾過(guò)程結(jié)束之后顆粒在膜面形成極薄的垢層,隨著反洗過(guò)程的進(jìn)行,以膜面污染顆粒的體積分?jǐn)?shù)變化來(lái)揭示膜面污染層的剝落過(guò)程。根據(jù)模擬運(yùn)算的結(jié)果,用三維圖形展示出反洗過(guò)程中膜反應(yīng)器內(nèi)的速度分布與變化,同時(shí)通過(guò)顆粒運(yùn)動(dòng)的分布特征對(duì)膜面污染層的動(dòng)態(tài)剝落過(guò)程進(jìn)行分析。CFD模擬結(jié)果表明:水力反洗能夠有效去除膜面的污染顆粒,并且隨著反洗過(guò)程的繼續(xù),膜面污染會(huì)被進(jìn)一步清除。在反洗過(guò)程中,出現(xiàn)了清洗的不均勻現(xiàn)象,研究結(jié)果表明膜絲上端具有最佳的清洗效果,其清洗程度優(yōu)于膜絲的中段,下端區(qū)域清洗效果最差。其次,通過(guò)CFD技術(shù)對(duì)氣體沖洗過(guò)程中膜反應(yīng)器內(nèi)的氣-液兩相流運(yùn)動(dòng)進(jìn)行了數(shù)值模擬,研究選取0.167m/s,0.387m/s,0.512m/s三種不同的氣體沖洗速度,對(duì)比了反應(yīng)器內(nèi)氣泡流的運(yùn)動(dòng)變化情況。分析膜面經(jīng)受的剪切力大小,同時(shí)結(jié)合反洗對(duì)膜絲不同區(qū)域污染去除效果的優(yōu)劣,從而確定最優(yōu)的氣體沖洗速度。通過(guò)分析最優(yōu)氣體沖洗速度下反應(yīng)器內(nèi)的速度和矢量等流體力學(xué)性質(zhì),得出膜絲的下端和中段部位具有較高的剪切力,能夠進(jìn)一步提高中空纖維中部以及下端的污染去除效果,并可有效阻止膜面濾餅的形成。此外,氣體沖洗能夠有效地作用于膜面反洗效果較差的區(qū)域,如膜絲位置0.25,0.275和0.425m處,進(jìn)一步去除這些區(qū)域的污染。這同樣也表明水力反洗后利用氣體沖洗能夠進(jìn)一步清洗中空纖維膜,并且減輕膜污染的不均勻分布。最后,通過(guò)混凝-膜過(guò)濾小試裝置的過(guò)濾及清洗實(shí)驗(yàn),對(duì)CFD模擬結(jié)果進(jìn)行驗(yàn)證。實(shí)驗(yàn)對(duì)比兩種不同的清洗方式(水力反洗、氣體沖洗)下的膜比通量(J/J0)及跨膜壓差,研究被污染中空纖維膜過(guò)濾性能的恢復(fù)狀況。研究發(fā)現(xiàn)相比單純的水力反洗,反洗結(jié)合氣體沖洗可更好抑制TMP的增長(zhǎng),且膜比通量的下降也相對(duì)緩慢。實(shí)驗(yàn)結(jié)果表明,反洗結(jié)合氣體沖洗的清洗方式能更有效的去除膜面污染,在更大程度上恢復(fù)膜性能,實(shí)驗(yàn)結(jié)論與模擬研究中氣體沖洗能夠進(jìn)一步去除膜面污染的結(jié)論相吻合。
[Abstract]:Membrane fouling limits the further application of hollow fiber membrane in water treatment, while hydraulic backwashing and gas washing can effectively alleviate the membrane fouling in the external pressure immersed hollow fiber membrane system. In this paper, the change of membrane fouling layer during backwash and the effect of shear force on membrane fouling during gas flushing are studied by means of computational fluid dynamics (CFD) simulation. In the simulation process, the membrane assembly placed in the geometry reflects the true size of the hollow fiber membrane, and there is a simplified aeration device at the bottom of the reactor to simulate the gas flushing process. In addition, the filaments are arranged in the porous media area instead of the sliding wall surface. Firstly, CFD numerical simulation was used to study the change of membrane fouling layer during hydraulic backwashing. Assuming that the particles form an extremely thin scale layer on the membrane surface after the filtration process, the spalling process of the fouling layer on the membrane surface is revealed by the change of the volume fraction of the fouled particles on the membrane surface with the process of backwashing. According to the result of simulation operation, the velocity distribution and variation in membrane reactor during backwash process are shown by three-dimensional graphics. At the same time, the dynamic spalling process of fouling layer on membrane surface is analyzed by the distribution characteristics of particle movement. The results of CFD simulation show that hydraulic backwash can effectively remove contaminated particles from membrane surface, and with the continuous backwash process, Membrane fouling will be further removed. The results show that the upper end of the membrane wire has the best cleaning effect, and the cleaning degree is better than the middle part of the membrane wire, and the cleaning effect of the lower end area is the worst. Secondly, the gas-liquid two-phase flow in the membrane reactor was numerically simulated by CFD technique. Three different gas flushing velocities, 0.167 m / s 0.387 m / s and 0.512 m / s, were studied and compared. The shearing force on the membrane surface was analyzed, and the effect of backwash on the removal of fouling in different areas of the membrane was analyzed, so as to determine the optimal gas washing speed. By analyzing the hydrodynamic properties such as velocity and vector in the reactor at optimal gas washing rate, it is concluded that the lower end and middle part of the membrane filament have high shear force, which can further improve the pollution removal effect of the hollow fiber in the middle and lower end. And can effectively prevent the formation of membrane filter cake. In addition, gas flushing can effectively remove the pollution in the areas where the backwash efficiency of the membrane surface is poor, such as the position of the filaments at 0.25m 0.275 and 0.425m. It also shows that the hollow fiber membrane can be further cleaned by gas flushing after hydraulic backwash and the uneven distribution of membrane fouling can be reduced. Finally, the CFD simulation results were verified by the filtration and cleaning experiments of the coagulation-membrane filtration plant. The membrane specific flux of J- / J0 and the pressure difference between the two different cleaning methods (hydraulic backwash and gas flushing) were compared and the recovery of the filtration performance of the fouled hollow fiber membrane was studied. Compared with pure hydraulic backwash, backwash combined with gas flushing can inhibit the growth of TMP and decrease the specific flux of TMP more slowly. The experimental results show that the backwash combined with gas washing can remove membrane surface pollution more effectively and recover membrane performance to a greater extent. The experimental results agree with the conclusion that gas flushing can further remove membrane surface fouling in the simulation study.
【學(xué)位授予單位】：天津工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TQ028.8

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